The invention relates to dissolving barium sulfate solid from locations in and around the boreholes of wells and/or other relatively remote locations into which a fluid can be flowed.
Various procedures for removing various type of scales with aminopolyacetic acid salt chelating agents, such as EDTA (ethylenediaminetetraacetic acid), have been known for at least about 30 years. For example, U.S. Pat. No. 2,396,938 (filed in 1944) describes removing boiler scale with aqueous solutions of such a chelant and an alkali meta hydroxide. U.S. Pat. No. 2,802,788 (filed in 1952) describes a radiator cleaning composition in which such a chelant salt is included in an aqueous solution along with an inorganic chelant, e.g., sodum tripolyphosphate. U.S. Pat. No 3,308,065 (filed in 1963)describes a substantially one-pore volume treatment for removing calcium sulfate-containing scale with an ammoniated or aminated chelant, e.g., an ammonium salt of EDTA. U.S. Pat. No. 3,660,287 (filed in 1967) describes a similar treatment for dissolving calcium sulfate-containing scale with a mixture of an EDTA salt and a water soluble inorganic carbonate salt. Such prior processes were consistent in utilizing an amount of solution which about filled one pore volume of the region within which the scale was to be removed and using a concentration of chelant such that that volume of the solution contained a stoichiometric excess relative to the amount of scale to be dissolved.